Well the first evident thing would be the negation of false color. Your images will also be more contrasy and snap into focus better. Having viewed through a 100ed for a while at a star party I can say that while your DSOs will be virtually identical the 100ed will have more contrast and the dual speed is a very nice thing to have.

Yes. You lose some contrast from CA since a few wavelengths of light are not entering your eye at the same point as the others. Of course it depends on how you look at it and if you can I'd suggest locating somewhere that you can have a look through one your self.

On DSOs not really, on anything bright - absolutely! The reduced CA will improve lunar and planetary performance and can even help when splitting doubles. The SW100ED Pro is a great deal at the regular price, with the big discount it's a cosmic no-brainer in my book

Not sure if the Ed100 will give you that much more on the moon. Luna is a very bright and high contrast object. I think what you want here is more aperture to get you more resolution and go deeper. I would think of getting a Newt, SCT or Mak for days where you want to go in deep and keep the ED80 for those grab and go days. A C6, for example, would ride nicely on your mount and give you enough aperture to make things more interesting, even during average seeing conditions. Yes some will tell you that it only has the contrast of a 4” refractor, but the moon has high contrast to start with, so this will be less critical. The extra resolution would nice. Otherwise you may want to hold out for the 120ED, especially since refractors are your favourite instruments. My two cents.

Thank you. What do you usually observe? DSO or lunar/planetary? What changed for you with the new scope?

Thanks!

I observe open clusters, globs, and dso's most, then planetary, and doubles least. There is a definite improvement in all of the above. I couldnt make out the adjoining galaxies to adromeda with the 102gt and i can with the ed100. Best analogy would be going from a lcd tv, to a top of the line 4k led tv. Same size, just a ton clearer.

Consider a 120ED type scope. If you really want a meaningful improvement, this is the way you should get it.

Changing from an f/10 achomat will of course make an improvement.

But here is the thing. Apeture gives you exit pupil.

A 100mm achromat is going to give you a dim image at 150x.

And guess what. So will a 100mm f/9 ED scope.

And exit pupil and image scale are your friends for planetary observing.

If you really want to improve your planetary observing, but retain all of the virtues of the refracting design (wide fields, no coma) then again, sell all your stuff and buy a telescope that is not only better, but is also bigger.

I know, the price is really nice, but I don't think you are going to pee your pants at the difference.

A 120ED scope though? Now you are talking.

Past this and it gets expensive fast, but the 120ED scopes were a tremendous value. They are still light and have a short enough package that they are not demanding to mount, and they will be much more capable planetary performers than a 100ED.

Do yourself a faver and take a step and a half ahead rather than a half step sideways.

And if you can't afford it now, then live with what you have until you can.

I would wait to afford the 120ED. However, if you are impatient then there is an Orion (Vixen) 120mm NeoAchromat for sale in the CN Classifieds with mount for $849. Reviews place it sharper than your 102 with about the same level of color correction,

I do not for the life of me understand how people can use an alt az mount for planetary observing.

Almost all scopes only perform at their full potential when the target is within a few arc minutes of the center of the field.

For reflectors, coma is the contrast killer if you let the planet get out of the center of the field by more than 5 or 6 arc minutes for a typical reflector. Beyond this and the image is no longer diffraction limited.

For refractors, it is field curvature. Once you let the target drift about 5 or 10 arc minutes out of the center of the field it is no longer at best focus.

For the highest resolution observing, it is really best to have the target at or near the center of the field.

And for planets, where you want to use high power, keeping the target centered is really important.

This allows you to relax and concentrate on the target.

Even today, using only 75x on my 110ED for solar white light, it was driving me mad to track (my motor drive is down for repair).

Just as I would get a few moments of steady seeing, I would be interrupted to re-center the target area. Seeing was coming and going and here I was taking my eye off the ball.

How maddening!

To me, if you are really serious about planets, you need a tracking mount.

You can get the CG4 for $275 brand new and shipped to your door.

This is not the most sturdy mount on the planet but is is not really much worse than a lot of Alt-Az mounts that cost $300.

I really mean this. For planets, I would rather have a mount that shakes when I focus it but has tracking than have a solid alt-az mount.

But that is me. I think I have done some really amazing planetary viewing, and I simply can't comprehend how people can eek the most challenging detail out of their scopes by being interrupted to move it every 30 seconds.

So, that is my take.

Sure, if you can afford a Cadillac mount like the GM-8, then that is great.

But my own advice is that if you really want to get the most detail out of a scope that is aimed at a planet, you need a good, comfortable observers chair and a tracking mount.

I think you can do some pretty good planetary observing with a good 120mm ED refractor (and I would not get the Vixen 120. It is not going to be in the same class as the 120ED scope).

But when you study optics, you quickly realize that most telescopes will perform at there very best when the target is kept very close to the center of the field.

And don't be fooled. Most refractors do defocus at the edge of the field, but as long as the star does not swell up to more than about 3 arc minutes of apparent field, we can't really tell that easily because in a coma free refractor, it remains a small dot.

But the planet will go out of focus and you can easily see it.

Sorry for the rant, but if you get a great planetary scope, get the most out of it with a tracking mount.

And later, get a good pair of binoviewers.

I have come to consider Binoviewers as far more important than the eyepieces you put in them.

These are all the opinions of an old man, but I have been doing serious planetary observing for a very long time now, and have had very great success I think.

And how people do serious planetary observing with an un-driven mount is beyond me.

Today, doing the sun without my motor was maddening. Every time I seemed to get a moment of perfect seeing, the detail seemed to be drifting close to the defocus point of the diffraction limited field of my scope. Maddening.

I said CG4 in my previous post, but there are other inexpensive GEMs if money is tight. You can get used CG5 type mounts for less than $300 too.

A really decent Alt Az is going to cost double this by the time you stick a good tripod on it.

I am running my new 110ED (14 lbs with binoviewer and eyepiece) on a humble Polaris mount (though it does have a HAL 110 tripod).

Sure it shakes a little when I touch it, but once I let go it settle down.

And planetary observing is about waiting a lot of times.

You pick the power that you think will give you the best result for the best moments of seeing that are occurring, plug it in, sit, and wait.

Most people make the mistake of using a power that gives the best overall view for the average of the seeing, but I always select the power that is right for the few moments of more stable seeing that always occur.

It is during these fleeting seconds that you get your most challenging detail.

And if you are fussing with eyepieces or with re-positioning the mount, you miss it.

This is the key to getting the most out of your telescope for planetary observing. Push the power a little big over what seeing seems to limit you to, sit, and wait for it.

It almost always comes.

Big scopes are not supposed to do well in most seeing, but all of my best observations were done in less than excellent seeing using the above method.

I would wait for the 120ED, the 100ED is too small for detailed planetary views.There are also 6" achromats to consider.

IMO there is a bulk/mount consideration when moving between a 4" to 5" class instrument that is not trivial. As far as details comparitively in a 100 vs 120 I'm not so sure I would chanracterize it as so dramatic for planetary. It's a 20% gain in resolution, which is about the same as going from an 85mm to a 102mm. So if the OP wants to get a flavor of a difference in details between a 100 and 120, all they have to do is make an 85mm mask for thair Celestron 102, point it at Jupiter, and observe with and without the mask to get an idea of the relative difference in resolution.

And as far as details, a 4" can see quite a bit. Below is what I see *typically" on average with Jupiter - boundry details are etched when viewing, my sketching skills not good enough to represent this well however. Last week at about 4:30am I got a peek of Jupiter that was far better than this in my 4" APO as the atmosphere was very clear and stable. This is a binoviewer sketch and the 4" APO was mounted on a simple Vixen PORTA II. Eyepieces and bino were not exotic either.

I don't think we need to get wrapped up with individual words. That's just my interpretation of things. So simply replace dramatic with one you think correct. My post where I quoted Seamark30 was in response to 2 things, one being that a "100ED is too small for detailed planetary". So by inference from that quote, which is quite proper, if a 100 is too small and a 120 is fine, I would personally chanracterize the difference between going from too small to acceptable as a dramatic one relatively. So that is where dramatic comes from, all contained within interpretation of what I quoted. So if that particular word is bothering, then my apologies and simply put in another word you want that charaterizes a situation where one aperture is inadequate by being too small and the other aperture of 120 is adequate. I will keep that relative difference as being dramatic for my perspective on things.

But again, let's not get wrapped up in the single word. My inclusion of the sketch is to indicate that 100 is indeed not too small at all, not by a long shot And going larger means lots of things, like beefier mounts and more effor and longer cool downs and of course much more money. I am trying to keep my responses atuned to the spirit of the OPs starting post. Talking all those other larger aperture instruments is way afield I think since the OP is asking about 100 vs 120 differences. I, btw, do care what the OP gets as they are asking advice afterall specific to a narrow request of 100mm vs 120mm.

As far as starting with "limited" capabilities, well all scopes have limited abilities and larger ones certainly limit lots of abilities relative to readiness. Heck, I've had SCTs that were never ready for planetary all evening long! Just one of their limitations in certain environmental scenarios. As far as MCTs, well I would expect RC to use that and tout it because he makes them, it is marketing afterall!

Anyway, none of these are chides, just another opinion for the OPs to consider. I personally don't think 100mm is too small and find it rewarding as my sketch shows. Larger is always better in *some* terms, but always has its downsides as well. The magic is in striking the balance that best meets individual goals